Mountain Iron | Minntac Taconite

Minntac Taconite facility

The Minntac Taconite facility produces taconite pellets near the city of Mountain Iron. MPCA efforts have focused on reducing the environmental impacts from the tailings basin, primarily through evaluation of treatment options, capturing and reusing surface discharges, and evaluating impacts to the surrounding groundwater. Much of this work was required through a series of enforcement actions with the ultimate goal of reissuing the permit with updated requirements that would bring the facility in compliance with all surface and groundwater standards.

Our role

The MPCA reviews and approves permits for water and air quality for mines in Minnesota. We have approved Minntac permits for:

  • NPDES/SDS water quality permit for operation of the tailings basin
  • NPDES/SDS water quality permit for mine pit dewatering discharges from its mining area
  • Air quality permits for air emissions from the mining area, processing facility and tailings basin

The most recent permitting effort for the Minntac tailings basin focused on specific steps to reduce the pollutant levels of the water within the tailings basin, resulting in a reduced concentration of pollutants in the seepage leaving the tailings basin. A draft permit was made available for public comment in November 2016. Revisions were made to the draft permit based on received comments and a proposed permit was sent to EPA for final review in November 2018. The final permit became effective December 1, 2018.


Minntac began production of taconite pellets in 1967 and is the largest taconite producer in North America with an annual production of up to 15 million long tons of pellets. Low-grade taconite iron ore of the Biwabik Iron Formation is extracted from a connected series of open pit mines stretching over an area of approximately eight miles long and up to a mile wide. The mined ore is then sent to the processing plant where it is crushed into a fine powder, concentrated by magnetic separation and flotation, formed into marble-sized balls, and then heated in large furnaces to form hardened pellets that are shipped to US Steel-owned blast furnaces in Indiana. The waste material from the crushing and concentration process, called tailings, are transported in a slurried form for disposal in the 8700-acre Minntac tailings basin just north of the plant. There, the tailings particles settle out and the water is recycled back for reuse at the plant.

Next steps and timeline

In April 2019, the decision to reissue the tailings basin permit was appealed by Fond du Lac Band, WaterLegacy and US Steel. In December 2019, Minnesota Court of Appeals reached a decision that resulted in the re-issuance of the permit being reversed. This decision was further petitioned by Fond du Lac, WaterLegacy and US Steel. Minnesota Supreme Court has not rendered a final decision.